The present invention relates to the decarbonylation of carbohydrates, including sugars, and to the simultaneous in-situ dehydrogenation and decarbonylation of alcohols, including sugar alcohols.
Metal complexes such as chlorotris(triphenylphosphine) rhodium and related compounds have been known to be useful as aldehyde decarbonylation agents. See, for example, U.S. Pat. No. 4,089,871; Osborn, J. A., et al., Inorg. Syn., 10:67-71 (1967); Baird, M. C., et al., J. Chem. Soc. (A), 348-351 (1968); Okno, K., et al., J. Am. Chem. Soc., 90:99-107 (1968); and Doughty, D. H., et al., J. Am. Chem. Soc., 100:7083-7085 (1978). However, insofar as these materials have been used in the decarbonylation of carbohydrates, their use has been limited to the decarbonylation of protected sugars. See, for example, Ward, D. J., et al., Chem. Ind., 162-163 (1976); Iley, D. E., et al., J. Am. Chem. Soc., 97:2563-2565 (1975); and MacCoss, M., et al., Tetrahedron Let., 26:4287-4290 (1985). See, also, Kruse, W., et al., Carbohyd. Res., 64:293-296 (1978) and Rajagopal, S., et al., J. Mol. Catal., 22:131-135 (1983), which suggest the deactivation of the hydrogenation catalyst RuCl.sub.2 (PPh.sub.3).sub.3 by the decarbonylation of glucose, but which do not identify the resulting sugar products.
This apparent prior limitation of the use of metal complexes to the decarbonylation of protected sugars is not surprising since: (a) it is difficult to find a common solvent for both free (unprotected) sugars and metal complexes that is sufficiently non-coordinating to prevent inhibition of the metal complexes and; (b) since most sugars exist in non-reactive cyclic hemi-acetal and hemi-ketal forms. In this latter regard, for example, it is known that the equilibrium composition of aqueous glucose is 99+% hemi-acetal and only about 0.002% free aldehyde sugar at room temperature. See, for example, Maple, S. R., et al., J. Am. Chem. Soc., 109:3168-3169 (1987) and Angyal, S. J., Adv. Carbohydr. Chem. Biochem., 42:15-68 (1984).